Reciprocating piston-cylinder combinations wherein fluid is alternatively supplied to and exhausted from alternate sides of a piston to provide power for driving the same in both directions is well known in the art. The prior art similarly recognizes certain valving control mechanisms for such piston-cylinder combinations wherein the introduction of an exhaust of fluid from respective sides of the piston is controlled by movement of the piston within the cylinder and such units normally include a mechanical connection between the piston and a vlave construction to reverse the total fluid flow. Typical prior art disclosing such units exits in U.S. patents to Lane, U.S. Pat. No. 1,067,613; Noack, U.S. Pat. No. 575,614; Pedroia, U.S. Pat. No. 2,698,710;
Paschke U.S. Pat. No. 3,691,907; and such a device is also disclosed in a co-pending application for U.S. patent, Ser. No. 1,305, filed Jan. 5, 1979 and entitled "Fluid Pressure Servo Detent Mechanism."
The cited patent references all provide similar fluid shifting controls or valving arrangements, and may even, as the co-pending application discloses, provide a utilization of the inlet fluid pressure to insure positive closing of the outlet valves of the unit.
With those skilled in the art, the effect of piston chatter of the unit is well known. Often, under minimal or no load conditions and occasionally under other load conditions, the valving structures do not completely open nor completely close at certain instances of their operation and the fluid flow to the piston is not smooth with a resulting chattering effect. A particular instance of such chattering is at that point when the piston begins to shift the valving structure. At this instance, fluid, unless positively controlled, is free to flow in either direction and should, for example, any of the valves be partially open or closed, fluid may be shuttled back and forth between passages to result in piston chatter and non-positive movement thereof.
With the assembly and valving disclosed herein, this condition is prevented and rather the valves are rapidly moved or "popped" into their proper next position. This condition is true even through, for example, the piston is in what may be termed a "stationary position" at the end of a stroke. Upon the piston causing any movement of the exhaust valving structure, fluid flow is controlled in such a manner that all valving is automatically and rapidly shifted to its next position to smoothly redirect the flow within the unit and therefore cause movement of the piston to the opposite end of the cylinder.